CPU Spy and Deep Sleep

I've just noticed that my tf201 does not go into Deep Sleep, but only manages 51 Mhz. Does anyone else have this? I can't identify which of the running apps might do this, but before expending the effort trying to, how different is Deep Sleep from 51 Mhz in terms of battery drain? My tablet usually spends around 90% of its time at 51 Mhz.

CPU Spy could be your issue in my opinion. I installed it to see if my tablet was rebooting without me knowing it. After that it rebooted so much it was almost unusable, uninstalled it and all was fine again. It definitely did some funky stuff with my TF101

TF101! - Running Domination built on my beautiful ArchLinux box!
Samsung Galaxy S4 - Stock Sadly...
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In the past I had this exact problem, which I eventually tracked down to a setting in Avast that kept the CPU running to scan for viruses after the device has been put to sleep - it's under Settings > CPU Wakelock.

Failing that, you might want to consider installing Better Battery Stats (or similar app) - these can give much more detailed information as to what is happening (you can set BBS to record what's going on when the screen is off, for example) and is how I identified the Avast! app as being the problem in my case.

In my case, keeping the CPU at 251Mhz all the time was consuming up to 50% of the battery overnight.

I'm not sure what the problem is, but it must be new and possibly hardware, as overnight from a full charge on both batteries, the dock's on 84% and the tablet's on 91%. I'm still only getting 51 MHz on CPU Spy. I've deleted quite a few apps. All the power management settings in ASUS customized settings are ticked. I even turned on Developer options, ticked them, unticked them and turned them off. I cold boot regularly. I don't think it happens if the unit is left turned off. I will confirm that.

Thanks, I will keep investigating. There are two issues, though. The steady drain on dock and tablet in standby, which is new, and the not going into Deep Sleep, which may be long-standing.

For the Deep Sleep I'll remove Apps until I solve it, but the new drain is puzzling. I guess it could be from a recent update, but I've noticed the charging behaviour when I charge them together has changed. It used to be that the dock would barely charge until the tablet was 100%. Now they charge in tandem (much as they drain in tandem).